The invention relates to a cross-bottom or block bottom valve sack of paper, plastic film or a similar foldable material especially for dusty or powdery material that is to be filled, with a filler valve, which is incorporated in the region of a valve-forming corner fold in one of its two sack bottoms, which are bounded at the sides by bottom side fold lines, said filler valve having a filter valve tube, which consists of a filter material that is permeable to gas yet retains the particles of the material to be filled, protrudes at one end over the valve-forming corner fold into the interior of the sack and can be pushed onto a filler connection piece of a pneumatic filling device.
When filling cross-bottom or block-bottom valve sacks of the material described, which are practically impermeable to air, with dusty or powdery materials using pneumatic filling devices, difficulties arise owing to the fact that the air, forced into the sack together with the dusty or powdery material, cannot readily escape into the open because of the impermeability of the sack material.
In order to provide a remedy here, various embodiments have been proposed, in which perforations and similar vent openings are disposed in the sack material. Admittedly, these permit the air to escape from the sack during the filling process. However, in the reverse way, they enable moisture to penetrate through the sack material into the contents of the sack. This is unacceptable, especially in the case of hygroscopic sack contents, which are to be protected by a moisture-barrier layer, which is included in the sack material in order to improve the shelf life of the contents.
In a cross-bottom or block-bottom valve sack of the initially stated type, which has furthermore become known, it is admittedly possible to do without perforations in the sack material for the purpose of venting the sack, since the filler valve itself here, due to the use of filter material for the valve tube, can bring about a venting of the sack during the filling process over the filter valve tube. At the same time, however, it turned out that the filter valve tube, pushed onto the filler connection piece of the filling device for carrying out the filling process, cannot surround the filler connection piece tightly while the sack is being filled in such a manner that air cannot by-pass the filter material and escape from the sack through the annular gap between the inner circumference of the filter valve tube and the outer circumference of the filler connection piece. By so doing, considerable proportions of the dusty or powdery material that is to be filled is carried along to the outside under some circumstances. This can cause considerable inconvenience to the operators of the filling device. Even small amounts of such dusty or powdery material, which is carried along to the outside, are unacceptable in most cases, especially if it is a question of packing chemical products with a certain health risk.